1. Field of the Invention
This invention relates to vehicle steering systems and, in particular, to a tie rod assembly and tie rod orientation used in a steering system.
2. Disclosure of Related Art
A conventional motor vehicle includes a pair of steered wheels disposed at opposite ends of a steer axle. Steering knuckles are rotatably supported on each end of the axle through kingpins or other conventional means and the wheels are supported on spindles that extend from the steering knuckles. The wheels are steered using a steering linkage that couples one of the steering knuckles to a steering gear that is in turn responsive to operation of a steering wheel in the vehicle. The steering knuckles are coupled together using a tie rod assembly so that the wheels are turned at coordinated angles during a turn.
In most conventional steering systems, the tie rod assembly includes a single tie rod linking the opposed steering knuckles. In vehicles having relatively large wheelbases, however, the ends of the tie rod often do not have sufficient clearance with the wheel or brake components such as the brake drums, brake discs, calipers, caliper mountings or brake dust shields found in conventional drum brake systems for the wheels. In order to provide sufficient clearance, optimal steering geometry is often sacrificed. Several steering systems have also been proposed in which the tie rod assembly includes a pair of tie rods linking the opposed steering knuckles. These conventional systems suffer from several disadvantages, however. First, the tie rod arms coupling the tie rod to the steering knuckle have generally varied in size, shape and/or configuration. As a result separate forging operations have to be performed for each of the tie rod arms thereby increasing tooling, inventory, and maintenance costs. Second, the outboard ends of the two tie rods continue to have insufficient clearance with the conventional wheel and brake components.
There is thus a need for a steering assembly that will minimize or eliminate one or more of the above-mentioned deficiencies.
The present invention provides a steering assembly for adjusting the steer angle of a pair of steered wheels on a motor vehicle and, in particular, a heavy truck.
A steering assembly in accordance with the present invention includes first and second tie rods. Each of the tie rods has an inboard end and an outboard end. The inboard ends of each tie rod may be coupled directly to a steering gear. Alternatively, the inboard ends of each tie rod may be coupled to a movable support member. The outboard ends of each tie rod are connected to the vehicle wheels and, in particular, may be connected to steering knuckles supporting the vehicle wheels. In accordance with the present invention, the inboard end of at least one of the first and second tie rods is located forward of the corresponding outboard end of the at least one tie rod relative to the forward direction of travel of the vehicle when the first and second wheels are facing forward.
A steering assembly in accordance with the present invention has several advantages as compared to conventional steering systems. First, the tie rod arms coupling the two tie rods to the steering knuckles may be identical in construction. As a result, a single forging operation can be used to produce both tie rod arms thereby reducing tooling, inventory, and maintenance costs. Second, moving the inboard ends of the tie rods forward of the outboard ends increases the effective length of the tie rod assembly (as defined by the distance between the outboard ends of the two tie rods) as the nominal wheel turn angle is increased. As a result, a single outboard end position for the tie rods can be used effectively over a wider range of wheelbases and/or the outboard end position of the tie rods can be located closer to the vehicle centerline and further from conventional wheel and brake components. This reduces the number and variety of tie rods required to accommodate variations in vehicle design and allows consideration of alternative positions and designs for wheel and brake components. Further, the increase in the effective length of the tie rod assembly reduces toe out as the wheels are turned and the resulting tire wear over a relatively large wheelbase range. Finally, the use of two tie rods that are approximately one half of the length of the single tie rod found in most conventional assemblies results in much higher tie rod natural frequencies that are well above the accepted range of brake sprag vibration. As a result, brake sprag may be eliminated as a limiting design criteria for tie rods.
These and other features and objects of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.